Developing emulsion for electrostatic images

ABSTRACT

1. A DEVELOPING EMULSION FOR USE IN DEVELOPING A LATENT ELECTROSTATIC IMAGE INCLUDING IN COMBINATION A TACKY ORGANOSOL LIPIDE PHASE COMPRISING THE FOLLOWING BY WEIGHT:   PERCENT HIGH MOLECULAR WEIGHT POLYMER 3.5-5.5 LIGHT HYDROCARBON LIQUID 32.0-52.0 PIGMENT 0.5-1.5   IN WHICH LSAID LIGHT HYDROCARBON LIQUID INCLUDES ABOUT 90% ISOPARAFFINIC HYDROCARBONS AND ABOUT 10% AROMATIC HYDROCARBONS, AND A DISPERSE AQUEOUS PHASE COMPRISING THE FOLLOWING BY WEIGHT:   PERCENT WATER 43.0-64.0 SURFACE-ACTIVE EMULSIFYING AGENT 0.01-0.15 ANTITOAM AGENT 0.01-0.15   SAID HIGH MOLECULAR WEIGHT POLYMER BEING DISSOLVED IN SAID AROMATIC HYDROCARBON LIQUID.

United States Patent Office 3,843,538 DEVELOPING EMULSION FOR ELECTROSTATIC IMAGES Marinus Cornelus Vermeulen, Valley View, Ian Edward Smith, Lockleys, and Peter John Hastwell, North Adelaide, Australia, assignors to Savin Business Machines Corporation, Valhalla, N.Y. No Drawing. Filed July 7, 1972, Ser. No. 269,603 Int. Cl. G03g 9/04 US. Cl. 252-621 4 Claims ABSTRACT OF THE DISCLOSURE An emulsion for developing electrostatic images comprising a disperse water phase and a continuous phase which is a solution of a pigmented high molecular weight polymer dissolved in an appropriate organic solvent. The emulsion is non-conductive, may be stabilized by a surface-active emulsifying agent which has a predetermined hydrophilic-lipophilic balance, and may include a protective colloid and a defoaming agent. If desired, a release agent may be employed in the continuous phase of the emulsion.

BACKGROUND OF THE INVENTION In our co-pending application, Ser. No. 155,108, filed June 21, 1971, for Method of Contact Transfer of Developed Electrostatic Images and Means for Practicing Same, we disclosed a developing liquid for developing a latent electrostatic image which comprised a solution of a high molecular weight resin substantially insoluble in a light hydrocarbon liquid, which solution is dispersed or suspended in such light hydrocarbon liquid. The light hydrocarbon liquid is adapted to be evaporated from a developed latent electrostatic image and to leave a tacky developed image on a photoconductive surface on which the latent electrostatic image is formed. The tacky image is adapted to be transferred to a sheet of paper or other sheet material by contact with the tacky image. After drying, the paper carries the final reproduction of the original. In order to assist in the transfer of the developed tacky toner image from the photoconductive surface to the paper surface, we disclosed that the photoconductive surface could 'be coated with a silicone or a urethane film in order to reduce the afiinity of the tacky developed image for the photoconductor and thus assist in the ready transfer of the image to the paper surface.

In our co-pendingapplication, Ser. No. 269,054, filed July 5, 1972, for Improved Developing Liquid for Electrostatic Images, We disclosed that a minor amount of release agent could be suspended in the carrier liquid. The release agent had to be insoluble in the carrier liquid and had to be of electrophoretic nature. It was taught that the carrier liquid had to be a light hydrocarbon since it must be non-conductive and so that it could evaporate readily to leave a diluent-free developed tacky image which could then be transferred. As the speed of operation of electrophotographic apparatus increases, more evaporated light hydrocarbons are discharged into the atmosphere tending to pollute it. The pollution problem becomes a serious one when one operates a machine using a light hydrocarbon liquid as a carrier at high speeds in closed areas.

We have succeeded in emulsifying a solution of an organosol with water, so that the diluent liquid is water which, when evaporated, will not pollute the atmosphere. When a latent electrostatic image is developed with our aqueous emulsion, the tacky toner is attracted to the charged portions, thus in effect breaking the emulsion Attor-neys docket number: Smith et al. Case 53.

3,843,538 Patented Oct. 22, 1974 locally. The released water can be squeegeed or blown from the surface of the photoconductor and the tacky toner image may be transferred to the paper as described in our co-pending application, Ser. No. 155,108.

A pneumatic assembly for removing excess developer liquid from photoconductive surfaces is shown in our co-pending application, Ser. No. 200,433, filed Nov. 19, 1971, and now US. Pat. 3,741,643.

Summary of the Invention One object of our invention is to provide an aqueous emulsion in which the oil phase comprises a solution of a tacky toner-that is, an organosol such as disclosed in our co-pending application, Ser. No. 155,108.

Another object of our invention is to provide an emulsion of a solution of a tacky toner and water, so that the pollution of the atmosphere caused by the evaporation of light hydrocarbons is substantially reduced.

Another object of our invention is to provide a stable emulsion in which the water phase is dispersed and in which the continuous phase is a solution of a pigmented high molecular weight polymer dissolved in an appropriate organic solvent.

Another object of our invention is to provide a developing emulsion of the W/O type. This can be employed with an organic photocoductive surface which is normally hydrophobic such as trinitro-fluorenone and polyvinyl carbasole coated on a conductive base such as vacuum-evaporated aluminum deposited on polyester film.

Another object of our invention is to provide an emulsion for developing latent electrostatic images formed on an inorganic photoconductive surface such as zinc oxide which has been coated with a hydrophobic layer such as silicone.

Another object of our invention is to provide an aqueous emulsion for developing latent electrostatic images having a predetermined hydrophilic-lipophilic balance, which is non-conductive and in which water is in the disperse phase.

Other and further objects of our invention will appear from the following description.

In general, the tacky or adhesive toner composition is the lipide component of the emulsion. It comprises a high molecular weight resin or mixture of high molecular weight resins dissolved in an organic solvent. In general the organic solvent comprises a light hydrocarbon liquid which includes about isoparafiinic hydrocarbons and about 10% aromatic hydrocarbons. The aqueous or water phase comprises distilled water and a dispersing agent of the surface-active type. The emulsifying agent must be more soluble in or better wetted by the lipide phase than by the disperse or aqueous phase. A defoarning agent and a protective col'oid may be added to the water phase. The emulsion may be formed in any appropriate manner, as by milling in a colloid mill, a homogenizer, or by sonic or utrasonic equipment.

More particularly, a lipide component is formed as follows:

EXAMPLE 1 The following materials:

37.5 grams PLIOLITE VTAC 40.0 grams SOLPRENE 1205 100.0 grams SOLVESSO are emulsified in a high-speed emulsifying mill together with 1000 grarns of ISOPAR G. PLIOLITE VTAC is a vinyl-toluene/acrylate copolymer manufactured by Goodyear Tire & Rubber Company, of Akron, Ohio. SOLPRENE 1205 is a copolymer of butadiene and styrene in the ratio of 75/25, manufactured by the solution polymerization process, and sold by Phillips Petroleum Company. ISOPAR G is an isomerized parafiinic hydrocarbon having a specific gravity of .75 at F. and is substantially 100% pure isoparafiinic hydrocarbon. It has a boiling range from 157 C. to 177 C. SOLVESSO is a hydrocarbon solvent manufactured by Standard Oil Company of New Jersey. It has an initial boiling point of 159 C. and a final boiling point or end point of 182 C. It comprises largely aromatic hydrocarbons and has a kauri-butanol number of 91.

A toner matching the organosol is then formed as follows. We take:

100.0 grams microlith black 12.5 grams reflex blue 25.0 grams PLIOLITE VTAC 25.0 grams SOLPRENE 1205 and add sufiicient toluol to achieve correct milling viscosity. This mixture is milled in a cavitation mill and 120 grams of the toner is added to the organosol circulating in the mill.

The aqueous phase is formed as follows:

125.0 grams of distilled water 0.5 grams of an antifoam agent such as ethylene oxide condensate of stearic acid 1.25 grams of starch (protective colloid).

The emulsion is then formed by taking 250 grams of this lipide component to which we add 7 grams of mineral turps and emulsify the lipide component with the aqueous component.

This is accomplished by milling the aqueous and lipide phases in a colloid mill for three minutes. This mill mix will produce images on a negatively charged photoconductor. The excess toner liquid is removed with a squeegee roller or by an air knife. When the image is formed, the emulsion is broken locally by the deposit of the lipide phase to form the desired reproduction. The Water phase forms droplets on the background area. These water droplets are removed by an air knife and leave the background of the photoconductor completely dry. It is to be noted that an emulsifying or dispersing agent was not used in Example 1. The emulsion was employed shortly after it was formed. The defoamer was used mainly to counteract the aeration of the milling which is undesirable.

EXAMPLE 2 The following organosol was formed. We mixed:

37.5 grams PLIOLITE VTAC 10.0 grams SOLPRENE 1205 100.0 grams SOLVESSO.

To this We added 240 grams of the toner component of Example 1 and 1000 grams of ISOPAR G. These were milled in a colloid mill for three minutes.

The Water component of this Example 2 was made as follows. We mixed:

400.0 grams distilled water 0.1 gram TRITON X-l14 0.1 gram antifoam agent.

TRITON X-1l4 is a surface-active agent having emulsifying, wetting and dispersing properties. It includes alkylaryl polyether alcohols, sulfonates and sulfates. It is a non-ionic type and is manufactured by Rohm & Haas Company. Its hydrophilic-lipophilic balance (HLB value) is 12.4. Its molecular weight is approximately 536 and its density is 8.8. Any appropriate antifoam agent can be used. One is manufactured by Dow, Corning and is a silicone defoamer that is effective in very low concentrations. Another silicone-base antifoaming agent is manufactured by Laurel Soap Manufacturing Company.

It is to be understood that any appropriate emulsifying agent may be employed to give stability to the emulsion. The emulsifying agent, however, must always be more soluble in or better wetted by the continuous or lip de phase than the disperse or aqueous phase. The surfaceactive emulsifying agents are neither completely hydrophilic nor completely *lipophilic. Another emulsifying agent is composed of polyoxyalkylene derivatives of sorbitane fatty acids.

The emulsion of Example 2 is manufactured by emulsifying grams of ISOPAR G with 250 grams of the organosol of Example 2 together with the water component of Eyample 2 just described. The emulsification may take place in a homogenizer, a colloid mill, or in a sonic or ultrasonic emulsifying apparatus. We have found that a colloid mill does not give as good an emulsifying action as an ultrasonic emulsifier. The better the dispersion, the higher may be the water-to-adhesive toner ratio. With a good emulsifying action, the ISOPAR G which is now used in the formulation may be materially reduced or eliminated completely, so that we Will em'ulsify a pigmented solution of a high molecular weight resin directly with Water, the latter being in the disperse phase.

The emulsion of Example 2 develops a latent electrostatic image on a negatively charged photoconductor. The emulsion is stable and will not conduct electricity. Since. the photoconductive surface is hydrophobic, the droplets of Water released during development are readily blown away by an air knife.

It will be observed that we are emulsifying the liquid developer described in our co-pending application, Ser. No. 155,108; with water and that the lipide phase is a suspension or emulsion of an organosol in a light hydrocarbon diluent. Accordingly, We have a complex system in which the lipide phase is a suspension of an organosol.

We are still conducting experiments in making emulsions with the object of reducing the isoparafiin or diluent component since this is what must be evaporated after the electrostatic image is developed. It will be seen, however, that we have greatly reduced the amount of isoparaifinic hydrocarbons which must be evaporated by our aqueous emulsion.

EXAMPLE 3 To the materials we mixed in Example 2 we add a release agent such as polyethylene wax, polyvinyl stearate, polyvinyl chloride resin, silicon resin, or reactive silicon fluid, in amounts varying between 4 grams and 14 grams by weight. The release agents are co-deposited with the organosol during development and assist in the transfer of the developed image from the surface of the photoconductor to the paper. These release agents are described in our co-pending application, Ser. No. 269,054, mentioned above. The use of a release agent not only assists in the complete transfer of the developed tacky image, but aids in keeping the photoconductive surface clean for a longer period of time. Furthermore, in the event the photoconductive surface becomes soiled, it is more readily cleaned when release agents are used.

It will be seen that we have accomplished the objects of our invention. We have provided an aqueous emulsion in which the organosol is in the continuous phase and in which Water is in the disperse phase so that, upon development of a latent electrostatic image, water instead of a light hydrocarbon liquid is released. This substantially reduces the pollution of the atmosphere which would be caused by the evaporation of a light hydrocarbon diluent as a carrier for the organosol toner.

The use of an emulsifying agent provides a stable emulsion, and the advantage of a release agent in the continuous phase assists in the complete transfer of the tacky developed image from the photoconductor to the paper or other sheet material.

It will be understood that certain features and subcom binations are of utility and may be employed without reference to other features and subcombinations. This is 1 See footnote 1.

contemplated by and is within the scope of our claims. It is further obvious that various changes may be made in details within the scope of our claims without departing from the spirit of our invention. It is, therefore, to be understood that our invention is not to be limited to the specific details shown and described.

Having thus described our invention, what we claim is:

1. A developing emulsion for use in developing a latent electrostatic image including in combination a tacky 0rganosol lipide phase comprising the following by weight:

Percent High molecular weight polymer 3.5-5.5 Light hydrocarbon liquid 32.0-52.0 Pigment 0.5-1.5

in which said light hydrocarbon liquid includes about 90% isoparaffinic hydrocarbons and about aromatic hydrocarbons, and a disperse aqueous phase comprising the following by weight:

Percent Water 43.0-64.0 Surface-active emulsifying agent 0.01-0.15 Antiioam agent 0.01-0.15

said high molecular weight polymer being dissolved in said aromatic hydrocarbon liquid.

2. A developing emulsion as in Claim 1 in which the lipide phase carries between 0.5% and 1.0% of a release agent.

3. A developing emulsion for use in developing a latent electrostatic image including in combination a continuous References Cited UNITED STATES PATENTS 3,156,531 11/1964 Fauser et al 25262.1 3,001,888 9/1961 Metcalfe et a] 25262.1 2,637,621 5/1953 Auer 862 2,594,899 4/ 1952 Fordemwalt 862 2,383,937 9/1945 Kienle et a1. 862 2,323,871 7/1943 Kienle et al. 862 2,307,097 1/ 1943 Anderson 862 3,301,698 1/1967 Fauser et a1 25262.1

OTHER REFERENCES Water as an Electrostatic Toner, Product ,Licenslng Index, March, 1972, pp. 46-47.

RONALD H. SMITH, Primary Examiner J. P. BRAMMER, Assistant Examiner 

1. A DEVELOPING EMULSION FOR USE IN DEVELOPING A LATENT ELECTROSTATIC IMAGE INCLUDING IN COMBINATION A TACKY ORGANOSOL LIPIDE PHASE COMPRISING THE FOLLOWING BY WEIGHT: 